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Sunday, 12 February 2012

Hell as Habitat, part 2

Last time, we left the hydrothermal vents as steaming chimneys of boiling volcanic water, liquid smoke and underground flame.

Minerals spew out and, through a process called chemosynthesis, bacteria are able to take poisonous hydrogen sulphide and make from it all the sugars they need for survival.

They flourish in this deadly atmosphere and provide a source of food for a whole host of animals. They rely on energy not from the Sun, but from Earth herself.

It's a community of life, sitting on a mat of bacteria atop a volcano. Makes that elephants on a turtle one sound quite reasonable, doesn't it?

Image: Ifremer

Giant Tube Worm
One of the most recognisable members of the hydrothermal vent community has a very intimate relationship with bacteria indeed. It's Riftia pachyptila, an annelid that can reach some 2.4 m (7 ft 10 in) long. That's the "Giant", the "Tube" is a chitinous structure they secrete for themselves to provide protection and support. They'll need it because they crowd around the vents in huge numbers, fixed in position and stationary forever more, come (lack of) Hell or high water.

From the white tube pokes out a beautifully deep red plume. It absorbs oxygen and carbon dioxide, and the colour comes from an unusual form of haemoglobin that allows them to absorb hydrogen sulphide without getting poisoned. But this isn't how they feed, this is just their side of the agreement.

Inside a special organ within their body, the Giant Tube Worm may have enough bacteria to make up half their body weight! It's the bacteria that uses that stuff absorbed by the plume, doing their nifty "food-from-poison" trick. Some of this is provided back to the worm, and the barter is complete. This is a lot like our very own Boneworm, who is in fact closely related.

Giant Tube Worms are one of the more dominant species in Pacific hydrothermal vents. The larvae are tiny and can drift for miles, perhaps making use of a digestive tract that they'll lose as they grow. And boy do they grow! In just 2 years, a completely new vent site can become covered in thousands of sexually mature, 1.5 m (4.9 ft) long Giant Tube Worms. This is thought to be the fastest growth rate of any marine invertebrate. I swear they grow faster than some worms move!

Image: Ifremer

Vent Crab
Crabs like Bythograea thermydron can always be seen scurrying around the forest of giant worms. They are probably unfussy eaters, a bit of scavenging here, preying there, grazing on bacteria and nipping at the plumes of the Giant Tube Worms.

Their larvae also drift and swim around to aid dispersal, at which point they have normal, crab eyes and researchers have found that they can be taken right up to the surface and survive just fine. Once into adulthood their eyes become naked retinas, which are much like eye-spots. These can see light emitting from the vent itself. They'll be 6 cm (2.4 in) across and unable to tolerate the feeble pressure near the surface.

Vent Eelpout
Also hanging out with the massive worms and taking the occasional nibble from their plumes (it must be like fruit trees for them) is Thermarces cerberus. Not too long ago I found out that Cerberus was a mythological, three-headed dog who guards the gate of Hades. Sounds about right!

They can be seen resting against rocks, all pale and tiny-eyed. They aren't proper eels, but they do have a long body with a long fin that goes from their back, all the way around their tail and halfway up their underside. They kinda look like tadpoles. Sickly tadpoles. A ghost of their former self, hanging onto a meagre sliver of life with grim determination, beady eyes blackened by hardship and struggle. So cute!

Image: Ifremer / A. Fifis

Yeti crab
Here's one that hails from an area between the southern tip of South America and Antarctica. It's called Kiwa hirsuta and "hirsute" is certainly the word! The legs and pincers are covered in what looks like rather luscious fur. It's a shame it's only 16 cm (6.3 in) long; a big hug from a giant Yeti Crab looks like it would be quite comforting.

But what is it all for, anyway? Not keeping warm in the cold, Southern Ocean that's for sure. The hydrothermal vents are about as warm a camp fire as you're ever gonna get. Instead, it houses bacteria that are thought to detoxify all the poisonous horrors coming out of the vent. It's not inconceivable that they could eat the bacteria too, but Yeti Crabs have been seen feeding on shrimp so eating their own bacteria might be a little desperate.

Also it's not a crab. It looks more like a squat lobster but it isn't one of those either. They've been given a whole new superfamily to frolic in, so "new kind of decapod" is probably the best description.

And of course, thank you to Dear Reader Kali who suggested I get onto the Yeti Crab. It, er... kinda got a little expanded from there!

Image: Ifremer / Dugornay

Pompeii Worm
Back to the Pacific and we find another extremist annelid. This time it's a polycheate worm who goes by the rather sensuous name Alvinella pompejana. These get to about 13 cm (5 in) long but bear several similarities to the Giant Tube Worm. They do live in tubes, but they're paper thin. They have haemoglobin-rich, red gills on their head. They even live in symbiosis with bacteria, but in a completely different way.

Pompeii Worms gather their own food, probably tiny microbes captured from the water. The bacteria reside on the worm's back, and the worm even feeds them with mucus secretions so they'll enjoy their stay and not leave because of the appalling catering. Clearly this disgusting, mouldy back is of the utmost importance to the worm. Why?

Well, Pompeii Worms can live with their tail-end resting in temperatures of up to 80 °C (176 °F). This makes them the second most heat tolerant animal in the world! Second only to the Water Bear, of course. The bacteria have a way to go to become the most heat tolerant micro-organism, but it's thought that they probably have something to do with the Pompeii Worm's amazing skills. It's a case of putting 2 and 2 together. And when at least one of those 2s is seriously nasty, the 4 had better be worth it!

Scaly-foot gastropod
Using bacteria is cool and all but those guys are just so DEMANDING! It's all "gimme gimme gimme". "I'm hungry. I'm thirsty. Are we there yet?" Bah! Crysomallon squamiferum has come up with an answer. Forget about "friendly" bacteria and natural eco-green whatever. Go for the chemicals.

Scaly-foot Gastropods incorporate iron sulphides into their shell for maximal next-gen protection against the elements. The foot is also armoured with ferocious looking scales of the same material. They only reach about 4 cm (1.6 in) long, but this Indian Ocean snail is built like a tank!

Smouldering wasteland of flaming death-poison? No problem! Predatory crab emerging from the shadows with angry death-face? Take a walk buddy! Hell has never been so safe! Available in Baleful Black and Whimsical White.

Image: NOAA Vents Program

Vent Mussel
Back to sessile creatures stuffed to the gills with bacteria. Vent Mussels like Bathymodiolus thermophilus can reach 20 cm across and live on hard rock. They again have lots of bacteria gaining energy from the sulphides and passing it on to the mussel. The larvae are again tiny and can drift along to find new places to set up home. When they do, they quite often end up creating massive clumps that provide a habitat for all sorts of other creatures.

It reminds me of the Pillar of Skulls in Planescape: Torment. That was a huge pile of angry, desperate dead-heads who knew a lot of stuff. They could pass on their knowledge. For a price. I don't think this mussel is an aphrodisiac or anything like that, so I don't know what kind of information they could provide you.

Image: Ifremer

Hot Water Volcano Octopus
Or Vent Octopus, Hydrothermal Octopus or whatever else. I don't care, because this octopus glories, GLORIES! under the name Vulcanoctopus hydrothermalis.

They have no irises in their eyes and seem to be blind. They have no pigment in their skin and appear translucent. They're tiny at 5.5 cm (2.2 in) mantle length, or 23.5 cm (9.3 in) when you include the tentacles. It's a proper little ghost! I don't know what it is with these black-eyed white things, somehow they are afforded instant charisma.

Vulcanoctopus tends to keep close to the aforementioned tube worms and mussels, hiding in the nooks and crannies if it feels threatened. It looks like they hunt by feeling around the place for crustaceans and so on. Feeding frenzies have been observed where they fight over swarms of amphipods.

No females have been spotted, but they have seen a male depositing his spermatophore. It's just that he was doing it with another male. Another male of a different species. Either this octopus is more profoundly blind than I thought, or that Mussel Mountain really is an extremely powerful aphrodisiac...